This invention is generally related to retractable tape rule assemblies and more particularly to rule assemblies of the spring retractable type.
A typical retractable tape rule assembly includes an elongated thin metal rule blade that is mounted on a reel rotatably disposed within a housing assembly. The rule blade is retracted into the housing assembly for storage by coiling it about the reel. A coil spring is mounted between the reel and housing assembly to provide spring powered rewinding of the blade about the reel to the fully retracted position of the blade after the measurement has been taken. Repeated extension and retraction is stressful on the blade, however. It has been found that the first several inches of the free end of the blade are particularly susceptible to damage and wear over the life of the tape assembly. The leading end of the blade is frequently handled, for example, by the tape assembly user to pull the tape out of the housing assembly or to hold the free end of the tape on the workpiece. This repeated handling of the free end of the tape exposes the numbering and graduation lines on the face of the tape to wear and over time can wear these markings off. Spring powered retraction of the blade may cause fairly rapid rewinding of the blade into the housing assembly, causing the last several inches of the rewinding tape (i.e., the several inches on the free end of the tape) to xe2x80x9cwhipxe2x80x9d or hit against the portions of the housing assembly that define the housing assembly opening. Over time, this hitting action of the tape against the housing assembly opening leads to cracks or tears in the tape and eventual tape breakage. Most breaks in the tapes of tape assemblies in commercial use occur in the first six inches of the blade.
Although tape breakage could be reduced by increasing the thickness of the metal of the blade, this is undesirable for several reasons. A thick blade increases tape assembly size, weight and material cost. A uniformly thick blade may have a detrimental effect on blade standout by increasing the weight of the extended portion of the blade. Furthermore, experience has shown that thickening or reinforcement of the entire blade length is not necessary to maximize service life of a rule assembly because most breaks and most blade wear occur in the several leading inches of the blade.
A need exists for a low cost, lightweight, durable material to cover and reinforce a selected length of a retractable tape blade that is easy to apply, highly durable and that can be used on any known tape rule product.
A retractable rule assembly comprising a housing assembly; a reel rotatably mounted in said housing assembly; an elongated blade formed of a ribbon of metal having one end connected to said reel, said blade extendable from a position tangential to said reel outwardly through a spaced opening in said housing assembly, said elongated blade housing a concavo-convex configuration when extended from said housing assembly, said elongated blade having measuring indicia formed on the concave side thereof, and a clear, protective coating provided on both said concave and convex side of said blade throughout the length of the blade for inhibiting wear of said measuring indicia; a coil spring formed of a ribbon of metal constructed to rotate said reel in said housing assembly in a direction to wind up the elongated blade when extending outwardly of said housing assembly opening in said concavo-convex cross-sectional configuration onto said reel in an abutting volute coil formation in a flattened cross-sectional configuration; and a blade holding assembly constructed to hold the blade in any position of extension outwardly of said housing assembly opening and to release the blade from any position in which it is held; a relatively short free end portion of said blade having a film of plastic material overlying said protective coating on at least one of the convex and concave side of the blade, said film of plastic material having a thickness greater than a thickness of said protective coating.
The thin film may be any flexible or semiflexible plastic such as thermoset, thermoplastic, thermoplastic elastomer or rubber materials. Preferably, the film is made of polyurethane and is adhered to the blade by an acrylic adhesive. Alternatively, a polyester, silicone, polyimides, polyethylene, fluoropolymers, Nylon(copyright) or Mylar(copyright) film could be used to cover the blade. Preferably, the film has a thickness dimension within a range of about 0.006xe2x80x3 to about 0.014xe2x80x3.
In one preferred embodiment the retractable rule assembly further includes an end hook member formed of sheet metal of a predetermined thickness to include a concavo-convex mounting portion and a U-shaped hook portion that is bent at a generally right angle from an end of the mounting portion. The end hook member is mounted on the free end of the blade with the mounting portion of the hook member being secured for limited movement with respect to the free end of the blade so that the rule can be measured externally from an exterior surface of the U-shaped hook portion or internally from an interior surface of the U-shaped hook portion. When the hook member is included, preferably the film is adhered to the concave side of the blade from the free end thereof a length that is within a range of from approximately 2xe2x80x3 to approximately 12xe2x80x3 so that one end portion of the film is disposed between the concave side of the blade and the mounting portion of the end hook member so that the portion of the tape on which the hook member is movably mounted is covered by tape.
The film of material provides localized strengthening and slight thickening of the blade to provide localized protection against cracking and breaking of the blade. The thin film also provides a transparent covering that can be used to cover the numbering and graduation lines on sections of the blade that are frequently handled. Because the thin film is very lightweight, it has no appreciable adverse effect on blade standout, even when it is applied on the first few inches of the blade.
It is contemplated to provide a wide range of tape assembly embodiments that include at least one section of the blade covered by a protective film as described above. More particularly, in the more specific aspects of the present invention, it is a further object to provide a retractable rule assembly having a blade that includes a protective film to provide the localized blade strengthening and protection previously described with any combination of the following additional features:
1. The blade has a blade width, thickness and height of concavoconvex curvature sufficient to enable the blade to stand out arcuately a length measured along the blade of approximately 11 feet with a horizontal linear length of standout thereof greater than 97% of the arcuate length of standout.
2. A retractable rule assembly wherein the elongated blade has a width in the flattened configuration thereof having a dimension within the range of 1.10xe2x80x3-1.5xe2x80x3, a height in the concavo-convex configuration thereof having a dimension within the range of 0.25xe2x80x3-0.40xe2x80x3 and a thickness in either configuration thereof having a dimension within the range of 0.0045xe2x80x3 to 0.0063xe2x80x3.
3. A retractable rule assembly wherein the concavo-convex cross-sectional configuration of the blade includes an arcuate central section having a predetermined radius of curvature and integral arcuate end sections each having the same radius of curvature, the radius of curvature of the central section being a dimension within the range of 0.35xe2x80x3 to 0.60xe2x80x3 and the radius of curvature of each end section being a dimension within the range of 1.0xe2x80x3 to 5.0xe2x80x3.
4. A retractable rule assembly wherein the metal ribbon of the spring has a width which is 95%-120% of the width of the metal ribbon of the blade.
5. A retractable rule assembly wherein the blade has an end hook member on the free end thereof, the end hook member being formed of sheet metal of a predetermined thickness to include a concavo-convex mounting portion having a U-shaped hook portion bent at a generally right angle from an end thereof, the end hook member being mounted on the free end of the blade with the mounting portion thereof secured in limited sliding engagement with a concave side of the free end of the blade so that the rule can be measured externally from an exterior surface of the U-shaped hook portion or internally from an interior surface of the U-shaped hook portion, the U-shaped hook portion including a bight section extending transversely from a convex side of the free end of the blade and spaced leg sections extending beyond transversely spaced corners of the free end of the blade.
6. A retractable rule assembly wherein the housing assembly includes a pair of cooperating housing members, each including an end wall having a peripheral wall extending from a periphery thereof and terminating in a free edge, the housing members being fixed together with their free edges interengaged by a plurality of bolts extending through one of the housing members and threadedly engaged in the other at spaced positions adjacent the peripheral walls thereof and by a fixed reel spindle having a non-circular interengaging recess-projection connection at each end thereof with the central interior of the adjacent end wall, each end of the spindle being interiorly threaded to threadedly receive a bolt therein extending through a central hole in the adjacent end wall and the recess-projection connection between the central hole and threaded interior.
7. A retractable rule assembly wherein the housing assembly includes a fitment defining a part of the housing assembly opening adjacent a convex side of the blade, the fitment having a plurality of tangentially extending transversely spaced elongated ridges defining surfaces for engaging the convex side of the blade extending tangentially from the reel to said housing assembly opening.
8. The housing assembly includes a bottom wall having an exterior portion at an end position adjacent the housing assembly opening which projects below the exterior surface portion extending therefrom toward an opposite end to provide a finger grip enhancing configuration.
9. The housing opening has a height dimension which exceeds the height dimension of the blade an amount that is at least approximately equal to the amount the hook portion extends below the bottom end surface of the housing assembly at the housing opening.
In the broadest aspects of the present invention, it is an object to provide any known tape rule product with a protective film along at least a portion of the blade as previously described.
These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.